1. Field of the Invention
The invention relates to an encoder, in particular to a carbon nanotube field-effect transistor encoder.
2. Description of the Related Art
An encoder is a combinational logic circuit for realizing conversion between different digitals. Due to the high precision, high resolution and high reliability of encoders, encoders are widely used in various encoding operations in industrial automation. At present, integrated chips of encoders are mostly based on the CMOS technology, and adopt binary CMOS gate circuits to realize their functions. With the improving integration level of chips and the reducing technological feature size, defects of the CMOS technology also become obvious, for example, the increment of leakage current, weakening performance and change stability. In addition, binary CMOS gate circuits adopt binary elements, and the quantity of information which is carried by binary signals (0, 1) is small. Therefore, the wiring area of encoder circuits increases, the structure of circuits is complex and the power consumption is large.
Compared to CMOS circuits, CNFETs have huge advantages. Compared to the deep submicron silicon technology, nonmetal carbon nanotubes with the trajectory transmission characteristic at the short-channel length of quasi-one-dimensional structure have smaller leakage currents and channel capacitance. Carbon nanotubes are to roll grapheme pieces into the tubular structure. Single-walled carbon nanotubes can shows metal characteristics and semiconductor characteristics. The good characteristics of carbon nanotubes with semiconductor properties have drawn electronic designers' wide attention. Therefore, in recent years, CNFETs have developed very fast. In the design of some simple circuits such as phase inverters, logic gate circuits and ring oscillators, CNFETs have successfully replaced CMOS circuits and the replacement has proved the availability of CNFETs.
Multi-valued logic circuits (for example, ternary logic circuits) have a large amount of information carried by each arranged wire, a small amount of input and output leads, the higher capacity of carrying information and a higher information density of integrated circuits, which can improve the utilization rate of space and time of circuits and effectively reduce the power consumption and cost of integrated circuits. Therefore, the design of a carbon nanotube field-effect transistor encoder which can convert binary signals into ternary signals is of great significance in improving the integration level of the encoder and reducing the cost and power consumption of the encoder.